migrate-mstest-v3-to-v4

# MSTest v3 -> v4 Migration Migrate a test project from MSTest v3 to MSTest v4. The outcome is a project using MSTest v4 that builds cleanly, passes tests, and accounts for every source-incompatible and behavioral change. MSTest v4 is **not binary compatible** with MSTest v3 -- any library compiled against v3 must be recompiled against v4. ## When to Use - Upgrading `MSTest.TestFramework`, `MSTest.TestAdapter`, or `MSTest` metapackage from 3.x to 4.x - Upgrading `MSTest.Sdk` from 3.x to 4.x - Fixing build errors after updating to MSTest v4 packages - Resolving behavioral changes in test execution after upgrading to MSTest v4 - Updating custom `TestMethodAttribute` or `ConditionBaseAttribute` implementations for v4 ## When Not to Use - The project already uses MSTest v4 and builds cleanly -- migration is done - Upgrading from MSTest v1 or v2 -- use `migrate-mstest-v1v2-to-v3` first, then return here - The project does not use MSTest - Migrating between test frameworks (e.g., MSTest to xUnit or NUnit) ## Inputs | Input | Required | Description | |-------|----------|-------------| | Project or solution path | Yes | The `.csproj`, `.sln`, or `.slnx` entry point containing MSTest test projects | | Build command | No | How to build (e.g., `dotnet build`, a repo build script). Auto-detect if not provided | | Test command | No | How to run tests (e.g., `dotnet test`). Auto-detect if not provided | ## Response Guidelines - **Always identify the current version first**: Before...